Stabilized hydrogen peroxide compositions

ABSTRACT

The present invention is directed to a hydrogen peroxide solution stabilized by ##STR1## wherein X is a linking group and Y is a metal cation or H which compound is soluble in hydrogen peroxide. In the second aspect of of the invention, a stabilized hydrogen peroxide solution contains a mineral acid which is suitable for etching a metal surface of a metal substrate such as a printed wiring board.

FIELD OF THE INVENTION

The invention relates to aqueous solutions containing hydrogen peroxide.A first aspect of the invention is an aqueous hydrogen peroxidecomposition comprising hydrogen peroxide stabilized by an organicstabilizer. A second aspect of the invention is an aqueous hydrogenperoxide-containing chemical etchant composition, useful in themanufacture of printed wiring boards, comprising hydrogen peroxide, anorganic stabilizer and a strong mineral acid.

BACKGROUND OF THE INVENTION

Hydrogen peroxide, H₂ O₂, is a commodity chemical used in manyindustrial processes. Hydrogen peroxide has been commercially availablesince the middle of the 19th Century in the form of aqueous solutions ofhydrogen peroxide within broad concentration ranges, typically between 1and 80 weight percent, and can be as concentrated as 96 weight percent.The major chemical properties and uses of hydrogen peroxide result fromits structure which includes a covalent oxygen-oxygen (peroxy oxygen)high energy-bond. The high energy peroxy bond provides the chemicaldriving force that makes hydrogen peroxide useful in many chemicalprocesses. More particularly, hydrogen peroxide is used in a variety oforganic and inorganic oxidation reactions, and can be used to make avariety of other organic and inorganic peroxy compounds. An importantuse for hydrogen peroxide is in the dissolution of metal, typicallycopper, from a masked printed wiring board substrate to form a finalwiring pattern. Typically the aqueous hydrogen peroxide etchantcompositions comprise in an aqueous solution, an active amount ofhydrogen peroxide, a strong mineral acid and an organic stabilizer.

While the high energy peroxy bond of hydrogen peroxide provides achemical driving force useful to chemists, the high energy bond can alsoresult in (1) the tendency of hydrogen peroxide to decompose into water,H₂ O and oxygen gas, O₂, and (2) the tendency to oxidize organiccompounds in the peroxide solutions. Highly pure hydrogen peroxide in asuitable inert container is relatively stable. However, commonlyavailable industrial grades of hydrogen peroxide are typicallycontaminated during manufacture, transfer, storage and use by chemicalimpurities that can catalyze or at least support decomposition. The mostcommon decomposition catalysts comprise di- or tri-valent metal ions.Stabilizers have been developed and are now commonly used to reducedecomposition to the lowest achievable level by minimizing the effect ofthe impurities. Examples of known stabilizing agents are8-hydroxyquinoline, sodium pyrophosphate, stannic acid, sulfolene,sulfolane, sulfoxide, sulfone, dialkylaminothioxomethyl,thioalkylsulfonic acids, aliphatic amines, benzotriazole,nitro-substituted organic compounds such as nitrobenzene sulfonic acids,thiosulfate, and others. Such stabilizers are known in a number of priorart publications.

Banush et al., U.S. Pat. No. 3,407,141, discloses an acid-hydrogenperoxide etchant solution containing an additive selected from the groupconsisting of phenyl urea, diphenyl urea, benzoic acid, hydroxybenzoicacid, and salts and mixtures thereof. Banush et al., further disclosesthat the etch rates and capacity of the solution are improved by addinga small amount of an additive such as sulfurthioazol.

Shibasaki et al., U.S. Pat. No. 3,773,577, discloses a sulfuric acid,hydrogen peroxide etchant solution containing an additive such asbenzotriazol.

Valayil et al., U.S. Pat. No. 4,233,111, discloses a sulfuric acid,hydrogen peroxide etchant solution containing a catalytic amount of3-sulfopropyldithiocarbamate sodium salt having the general formula##STR2## wherein R can be a C₁ -C₄ alkyl, a phenyl, a C₇ -C₁₀ alkaryl ora C₇ -C₁₀ aralkyl.

As an etchant for the manufacture of printed wiring boards, aqueoushydrogen peroxide solutions are attractive because hydrogen peroxidesolutions are relatively easily handled, have high activity and lowcost. However, hydrogen peroxide metal etching compositions can besubject to numerous problems and pitfalls. Since large amounts ofmetallic ions are generated during etching, the metallic ions canpromote rapid hydrogen peroxide decomposition, thus destroyingsubstantial proportions of the hydrogen peroxide that shouldeconomically be used directly in the removal of metal from printedwiring board circuits. Etchants that can be stabilized, during storageand use, from substantial decomposition of hydrogen peroxide aredesirable for convenient and effective etchant processes. Further, theetchant compositions should be stabilized from loss of the organicstabilizers. Still further, the rate of etching using hydrogen peroxideetchants can be accelerated using organic promoters.

BRIEF DESCRIPTION OF THE INVENTION

Useful hydrogen peroxide solutions, including bulk hydrogen peroxidecomprising a major proportion of hydrogen peroxide and aqueous workingsolutions of hydrogen peroxide, such as those used in etching printedwiring boards, can be stabilized to preserve the active concentrationsof hydrogen peroxide and an additional organic stabilizer, if present,in solution by incorporating in such solutions an effective amount of anorganic stabilizer additive comprising a sulfonic acid compound. Afterpreparation, solutions containing such an additive composition exhibitexceptional storage life without substantial peroxide or stabilizerdepletion over extended periods. Further, such solutions, containingsuch additives, effectively and efficiently etch metals including copperat high rates, high capacity, and have a long, active, useful etchinglife. It has further been found that combining other organic stabilizercompounds with an effective amount of the sulfonic acid compound in theperoxide solutions provides an added degree of protection againstperoxide decomposition. The particularly preferred solutions of theinvention comprise hydrogen peroxide and an effective combination of a3-(benzothiazoyl-2-thio)alkylene sulfonic acid compound in combinationwith sulfanilic acid compound.

SUMMARY OF THE INVENTION

The present invention is directed to a hydrogen peroxide solutionstabilized by a compound of the following formula: ##STR3## wherein X isa linking group and Y is a metal cation or H which compound is solublein hydrogen peroxide. A preferred linking group of Formula I is asubstituted alkyl wherein the alkyl moiety contains 1 to 13 carbon atomssuch as ##STR4## wherein R₁ and R₂ independently of the other are H orC₁₋₉ alkyl or a C₅ or C₆ saturated or unsaturated cyclic group and m andn independently of the other are an integer of 0 to 9, with the provisothe sum of m and n is not greater than 12.

In a second aspect of the invention, the stabilized hydrogen peroxidesolution contains a mineral acid which is suitable for etching a surfaceof a substrate such as a printed wiring board.

DETAILED DESCRIPTION OF THE INVENTION

Hydrogen peroxide solutions in bulk storage can comprise concentrationsof hydrogen peroxide that range from about 30 to about 95 weightpercent. Typically, such bulk hydrogen peroxide solutions contain aneffective amount comprising about 0.01 to about 5 weight percent of anorganic stabilizer and the balance typically comprises water. In usetypically such bulk hydrogen peroxide solutions are diluted. Water,solvents, and other chemical compositions can be added to the hydrogenperoxide solution in order to create a working peroxide composition.

In the present invention, an organic stabilizer is replaced at leastpartially by an organic stabilizer of Formula 1 referred to under theSummary of the Invention. In such Formula 1, it is considered that Y isordinarily present as hydrogen rather than an metal cation, but thecation form, e.g., a salt, can be introduced as a starting material. Apreferred linking group of Formula I, i.e., X, is a substituted alkylwherein the alkyl moiety contains 1 to 13 carbon atoms. A more preferredlinking group is presented in Formula II wherein R₁ and R₂ groups arehydrogen or C₁ to C₄ alkyl such as propyl and where R₁ and R₂ are thesame. Preferred m and n groups are identical and are 4 or less.

Examples of the organic stabilizer compounds includebenzothiazoyl-2-thiomethylene sulfonic acid,2-(benzothiazoyl-2-thio)ethylene sulfonic acid sodium salt,3-(benzothiazoyl-2-thio)propylene sulfonic acid potassium salt,12-(benzothiazoyl-2-thio)dodecylene sulfonic acid,3-(benzothiazoyl-2-thio)-(2-methyl)propylene sulfonic acid,4-(benzothiazoyl-2-thio)cyclohexylene sulfonic acid.

Since the Formula 1 compound functions to stabilize the hydrogenperoxide, that is reduce its rate of decomposition, the additive shouldbe soluble in the hydrogen peroxide at the concentration employed. Theconcentration of Formula 1 additive is not considered critical andillustratively is in the range of prior art stabilizers, for example0.01 to about 5 weight percent on the basis of hydrogen peroxide, water,and the Formula 1 stabilizer. For purposes of cost it may be desirableto introduce a second lower cost stabilizer such as one known in theprior art. An example of preferred stabilizer is a sulfanilic acidcompound of the following formula: ##STR5## wherein R1 and R2independently of the other comprises hydrogen or a C₁₋₁₀ linear orbranched chain alkyl group wherein R1 and R2 independently of the othercomprises hydrogen or a C₁₋₁₀ linear or branched chain alkyl group and Mis hydrogen or a metallic cation such as sodium potassium, calcium,copper. Sulfanilic acid, wherein each R is hydrogen(aminobenzenesulfonic acid), is the preferred co-additive.

An etching solution can contain in a major proportion of water, aneffective etching amount of hydrogen peroxide, a strong mineral acidsuch as sulfuric acid and the organic stabilizer composition of thisinvention.

Strong mineral acids that can be used in the etchant compositions of theinvention include sulfuric acid, nitric acid, hydrochloric acid,hydrofluoric acid, and fluoroboric acid.

While these solutions are particularly useful in the chemicaldissolution or etching of copper and copper alloys, other metals andalloys may also be dissolved with the chemical action of the solutions,for example iron, nickel, zinc, lead, or tin.

The etchant solutions of the invention can be made by diluting thehydrogen peroxide bulk solutions of the invention to the appropriatehydrogen peroxide concentration in typically aqueous media and addinganother necessary etchant compound such as the mineral acid.

Solvents which are useful in maintaining the organic stabilizer of theinvention in solutions include solvents which are soluble in water andwhich promote the solubility of the organic stabilizers of theinvention. Typically solvents useful in this invention includeoxygenated solvents and other highly polar solvents having high dipolemoments. Particular examples of useful solvents include methanol,ethanol, isopropanol, tetrahydrofuran, dimethylformamide,dimethylsulfoxide, and others.

In use the etchant solutions of the invention are formulated to dissolvemetal, commonly copper, at conventional etching conditions. The etchantsof this invention can be used in an environment in which chemical metalremoval is useful. Most commonly such etching processes are used in themanufacture of printed wiring (printed circuit) boards.

In the manufacture of such printed wiring boards, a photosensitiveresist is applied to a metal clad board or a laminate for multi-layeredboards. The board is masked and exposed to electromagnetic radiation ofan appropriate wave length for the resist. The use of the mask protectscertain resist areas from the effects of the light. In areas notprotected by the mask, the radiation typically causes the photoresist tocrosslink or polymerize, rendering the resist more chemically insoluble.Positive resists can also be used with an appropriate mask. Typicallythe exposed resist remains on the board while the unexposed resist caneasily be removed by a chemical rinse. After removal, the resist exposesunwanted areas of metal to chemical etching.

Typically the metal is etched at temperatures that range between about105 degrees to about 200 degrees Fahrenheit, and preferably for ease ofoperation 110 degrees to 140 degrees Fahrenheit. The solutions of thisinvention have sufficient activity for use in either immersion or sprayetching techniques. Etch rates obtained using the composition of theinvention can range from about 1 to 2 ounces of copper per square footper minute. After etching, the printed circuit board is typically rinsedwith water, the photoresist removed, and a single or double sidedprinted circuit board is directed to an assembly station.

To further illustrate the present invention the following examples areprovided.

EXAMPLE

Into a 2-liter glass beaker equipped with a magnetic stirrer was added600 milliliters of deionized water. Stirring was initiated and into thedeionized water was added 150 milliliters of 15 weight percent aqueoussulfuric acid. The mixture was agitated until uniform and into thestirred aqueous solution was added 50 milliliters of 50 weight percentactive aqueous hydrogen peroxide. Into the aqueous bath was placed 75grams of copper sulfate pentahydrate (CuSO₄.5H₂ O) and one of thefollowing:

(I) 0.75 grams of 3-(benzothiazoyl-2-thio)propylene sulfonic acid

(II) 0.25 grams of 3-(benzothiazoyl-2-thio)propyl sulfonic acid sodiumsalt and 0.5 grams of sulfanilic acid.

When uniformity in mixing was obtained, additional water was added toreach a total volume of 1,000 milliliters.

The 1 liter etchant baths of the Example were heated to 50 degreesCentigrade in a water tank heater. The solutions were maintained at thistemperature for 49 hours and the concentration of the hydrogen peroxideand the concentration of the organic stabilizer was monitored. Thefollowing Table sets forth the change in peroxide concentration.Additionally, the stabilizer concentration was measured after 49 hoursto determine if the concentration of stabilizer had decreased due todecomposition.

                  TABLE                                                           ______________________________________                                                                Change in                                                                     3-(benzylthiozoyl)-2-                                           Decrease in H.sub.2 O.sub.2                                                                 thio)propylene                                                  (g/L)         (mM) Units                                            Stabilizer                                                                              31.5 Hrs     49.0 Hrs 49.0 Hrs                                      ______________________________________                                        I         1.03         1.98     --                                            II        --           5.5      0.57                                          ______________________________________                                         g/L means grams per liter                                                     mM means millimoles                                                      

What is claimed is:
 1. A stabilized hydrogen peroxide compositioncomprising hydrogen peroxide and a compound of the following formula:##STR6## wherein X is a linking group and Y is a metal cation or H whichcompound is soluble in hydrogen peroxide.
 2. The composition of claim 1wherein X is a substituted alkyl wherein the alkyl moiety contains 1 to13 carbon atoms.
 3. The composition of claim 1 wherein X is of theformula: ##STR7## wherein R₁ and R₂ independently of the other are H orC₁₋₉ alkyl or a C₅ or C₆ saturated or unsaturated cyclic group and m andn independently of the other are an integer of 0 to 9 with the provisothe sum of m and n is not greater than
 12. 4. The composition of claim 3wherein R₁ and R₂ are the same and are H or a C₁ -C₄ alkyl.
 5. Thecomposition of claim 1 wherein Y is hydrogen.
 6. The composition ofclaim 3 wherein Y is hydrogen.
 7. The composition of claim 1 whichcontain a sulfanilic acid compound.
 8. An aqueous chemical etchantcomposition which comprises:(a) water (b) hydrogen peroxide (c) mineralacid (d) a compound of the formula: ##STR8## wherein X is a linkinggroup and Y is a metal cation which compound is soluble in hydrogenperoxide.
 9. The composition of claim 8 wherein X is a substituted alkylmoiety wherein the alkyl moiety contains 1 to 13 carbon atoms.
 10. Thecomposition of claim 8 wherein X is of the formula ##STR9## wherein R₁and R₂ independently of the other are H or C₁₋₉ alkyl or a C₅ or C₆saturated or unsaturated cyclic group and m and n independently of theother are an integer of 1 to 9 with the proviso the sum of m and n isnot greater than
 12. 11. The composition of claim 10 wherein R₁ and R₂are the same and are H or C₁ -C₄ alkyl.
 12. The composition of claim 8wherein Y is hydrogen.
 13. The composition of claim 10 wherein Y ishydrogen.
 14. A method of etching a surface containing metal comprisingetching a surface containing a metal portion with a composition whichcomprises:(a) water (b) hydrogen peroxide (c) mineral acid (d) and acompound of the formula ##STR10## wherein X is a linking group and Y isa metal cation or H which compound is soluble in hydrogen peroxide.